C8-alkylaromatic isomerization process



United States Patent U.S. Cl. 260-668 4 Claims ABSTRACT OF THEDISCLOSURE Ethylbenzene contained in a C -aromatic stream is effectivelyisomerized to xylene isomers by carefully controlling the C -naphthenecontent in said stream in an amount of about 2 wt. percent to about 9wt. percent of the C -aromatics contained in said stream.

CROSS-REFERENCES TO RELATED APPLICATIONS This application is acontinuation-in-part of our copending application Ser. No. 692,655,filed Dec. 22, 1967, now abandoned.

BACKGROUND OF INVENTION This invention relates to a C alkylaromaticisomerization process. More particularly, this invention relates to animproved C -alkylaromatic process wherein ethylbenzene is effectivelyisomerized to xylenes without incurring excessive (l -aromatic crackingand hydrogenation loss.

Processes for the production of the various xylene isomers have acquiredsignificant interest and importance within the petroleum andpetrochemical industries. Currently, this interest stems from the demandfor paraxylene as an intermediate for the synthetic fiber and fabricindustry.

Several currently available processes are effective for isomerizing onlythe xylene isomers and not the ethylbenzene C -ar0matic isomer. Attemptsto isomerize ethylbenzene to xylenes result in cracking losses whichrender the process economically unfeasible.

, DESCRIPTION OF "PRIOR ART In the prior art, Holm, US. Pat. No. Re.25,753 describes a method for isomerizing a non-equilibrium mixture ofxylenes and ethylbenzene towards equilibrium. Essentially, the methodrests upon the hypothesis that the co-existance of the correspondingnaphthenes is essential to the success of the method. Attention isdirected toward a two-step process in which hydroisomerization andsubsequent dehydrogenation are segregated, but data are also g ven for aone-step process in which from about 10 to 30 percent of the C cyclicsare naphthenes. These data show varying degrees of approach toequilibrium para- Xylene in total xylenes which depends upon the depthof simultaneous hydrogenation of the aromatic. It would appear from thedata presented, especially run numbers 3,538,173 Patented Nov. 3, 19704-1232 and 4-1214 of the Helm patent, that although para-xylene/xyleneconcentrations of about 21% and 25% respectively were obtained,saturation of C -ar0- matics was 10 and 35% respectively. It is notedthat equilibrium para-xylene/xylene concentration at these conditions isapproximately 24% SUMMARY OF INVENTION We have found, however, that acareful selection of processing conditions and catalyst will givesubstantially equilibrium para-xylene/xylene and ortho-xylene/Xyleneconcentrations, while saturating only a very minor portion of the C-aromatics to naphthenes, when attempting to isomerize ethylbenzene oran ethylbenzene-containing xylene stream. By substantial equilibrium wemean an approach to at least 90% of the para-xylene/xylenes in thereactor efiluent. Ortho-Xylene equilibrium is a little more diflicult toachieve. Hence, if ortho-xylene is the desired product from an orthodeficient feed, the term substantial equilibrium in this case would meanat least of the equilibrium value predicted for the orthoxylene mixture.The generally accepted equilibrium values (based on API sources) aretabulated below for our range of interest.

Temperature, K 600 700 800 Temperature, C 327 427 527 Mole percent ofisomer (including ethylbenzene):

Ethylbenzene 6 8 l1 Paraerylene... 22 22 21 Meta-xylene l 50 48 45Ortho'xylena 22 22 23 Mole percent of isom xylenes only) Para-xylene 2424 23 Meta-xylene 54 52 51 Ortho-xylene 22 24 26 brium between the C-aromatics and the C -naphthenes in the presence of added hydrogen isreadily adjusted by changing temperature, hydrogen ratio, or pressure.These conditions are so correlated that the naphthene content can beraised by either lowering temperature and/or raising pressure. Likewise,by either raising temperature and/ or lowering pressure, the naphthenecontent may be lowered.

When isomerization only among the xylenes is desired, without conversionof ethylbenzene to xylenes, only a trivial amount of C -naphthenes arerequired, but when ethylbenzene conversion to xylenes is desired, thenthe range of 2% to 9% C -nap'hthenes based on c -aromatics is essentialfor efficient operation. Thus, a feed stock rich in ethylbenzene, whichis by far the most common feed available from catalytic or pyrolyticsources, can be utilized. The advantage of this in commercial operationis that, instead of having, for example, 30% additional feed asnaphthenes, recycling through the isomerization system, a value of lessthan 10% naphthenes is completely adequate and makes for a moreefiicient and economical process. The advantage of the process of ourinvention is that we have obtained very high efficiencies in convertingethylbenzene to xylene isomers without incurring naphthene formation ofgreater than 10%. This also will be shown in great detail in theaccompanying examples.

Therefore in an embodiment, this invention relates to an isomerizationprocess for the production of a specific xylene isomer which comprisescontacting hydrogen and a C aromatic charge stock containingethylbenzene at a concentration greater than equilibrium with respect tothe xylenes present and containing C -naphthenes at isomerizationconditions in a reaction zone, with a catalytic composite of aluminacombined with about 0.01% to about 1.0% by weight of platinum componentand about 0.1% to about 5.0% by weight of a halogen component,separating a specific Xylene isomer from the resulting reaction producteffluent and providing a hydrocarbon stream containing unreactedethylbenzene, C -naphthenes and xylene isomers, and recycling saidhydrocarbon stream to said reaction zone; said process furthercharacterized in that said isomerization conditions are selected tomaintain a C -napthene content in said C -aromatic charge to saidreaction zone of from 2.0% to about 9.0% by weight of the C -aromaticsin said charge.

In further more limited embodiments said isomerization conditionsinclude an LHSV of about 0.2 to about 8.0, a temperature of about 370 C.to about 450 C., a pressure of about 3 atmospheres to about 20atmospheres, and a hydrogen concentration in a mole ratio of about 2.0:1to about 20.0:1 with respect ot said C -aromatic charge. In addition,1.0 to about 1000 p.p.m. by weight halogen may be added to said C-aromatic charge.

More specific embodiments and conditions will be found in the followingmore detailed description of this invention. As used herein, C -aromaticcharge stock refers to the charge stock fed to the isomerizationreaction zone. As is known to those trained in the art, the fresh feed,before being fed to the reactor may be first separated to recover aspecific xylene isomer before it is passed to the reactor or the freshfeed may be combined with a recycle stream and fed directly to thereactor.

DESCRIPTION OF PREFERRED EMBODIMENTS The process of our invention isapplicable to certain hydrocarbon fractions containing ethylbenzene inan amount above its equilibrium value where an object of the inventionis to produce one or more of the xylene isomers therefrom. The chargingstock may be ethylbenzene alone or ethylbenzene in admixture with ortho,meta-, or paraxylene, or a non-equilibrium mixture of the aforesaid C-aromatic hydrocarbons in which the ratio of isomers is other than theequilibrium portion of C aromatic components, said mixture being eitherexclusively C -aromatic components or accompanied by other classes ofhydrocarbons such as paraflins, other aromatic hydrocarbons, olefins,naphthenes, etc., or a mixture of hydrocarbons including at least one ofthe aforesaid xylene isomers with other compounds inert in the presentprocess. One of the preferred sources of the present charging stock is afraction derived from certain petroleum conversion products containingaromatic hydrocarbons and including fractions boiling within the rangeof from about 120 to about 145 C. Suitable fractions utilizable in theprocess may be separated from gasoline produced by subjecting anappropriately boiling petroleum fraction to dehydrogenation as forexample, a hydroformed gasoline boiling range fraction containingnaphthenic hydrocarbons. Such gasoline boiling range fractions may beproduced either thermally and/ or produced in a catalyzed cracking,reforming, or hydroforming reaction in accordance with procedures wellknown to the art.

The isomerization takes places in an isomerization zone maintained at aliquid hourly space velocity within the range of 0.2 to 8, andpreferably within the range of 0.6 to 3, a temperature within the rangeof 370 C. to 450 C. and preferably within the range of 380 C. to 440 C.,and a pressure within the range of 3 to 20 atmospheres and preferablywithin the range of to 18 atmospheres in the presence of not less than2.0 nor more than 9 weight percent C -naphthenes, and preferably in therange of 3 to 8 weight percent. A molal excess of hydrogen shall befurnished to the isomerization zone, usually in the range of about 2.0to 20 moles of hydrogen per mole of hydrocarbon feed.

The catalyst utilized in the present process comprises alumina, aplatinum component, and combined halogen with said catalyst beingdisposed within the reaction zone. The alumina support may be a highsurface area alumina such as gamma-, eta-, and theta-alumina, althoughthese are not necessarily of equivalent suitability. By the term highsurface area is meant a surface area measured by surface area techniqueswithin a range of from 25 to 500 or more square meters per gram, andpreferably a surface area of approximately to 300 square meters pergram.

The platinum component of this catalyst for use in our invention willnormally be utilized in an amount of from about 0.01 to about 1.0% byweight based upon the solid support. Of the various halogens which maybe utilized, both fluorine and chlorine can be used satisfactorilyeither separately or together. Normally, the halogen content of thecatalyst ranges from 0.1% to 5% by weight, and preferably from 1% to 4%,also, it is contemplated within the scope of this invention that halogenin an amount of from 0.0001 to 0.1% by weight of feed, and preferably inan amount of from about 0.001 to about 0.05% by weight of feed may becontinuously added to the isomerization zone. We have unexpectedlyfound, when using this p1atinum-alumia-combined fluorine catalyst, thatchlorine, in the range of from 0.001 to 0.05% by weight of feed is offeed may be continuously added to the isomerization of our invention.This halogen can be added by any suitable halogen-containing compoundsuch as t-butylchloride.

As will be recognized by one skilled in the art, the process of thisinvention utilizing the catalyst hereinbefore set forth may be effectedin any suitable manner and may comprise either a batch or continuousoperation, The preferred method by which the process of this inventionmay be effected is the continuous type operation. Thus, a particularlypreferred method of the fixed bed operation is one in which anon-equilibrium C -aromatic hydrocarbon fraction is continuously chargedto the reaction containing the fixed bed of the desired catalyst, saidzone being maintained at the proper operating conditions of temperatureand pressure as described above. The reaction zone may comprise anunpacked vessel or coil or may be lined with an adsorbent packingmaterial. The charge may be passed through the catalyst bed in anupward, downward, or radial flow and the isomerized product may becontinuously withdrawn, separated from the reactor effiuent andrecovered, while any unreacted starting materials may be recycled toform a portion of the feed stock to the reaction zone. It is within thescope of this invention to recover one or more specific xylene isomersas a product; for example, the process may be designed to producepara-xylene and/or ortho-xylene.

EXAMPLES The following examples are introduced for the purpose ofillustration only with no intention of unduly limiting the generallybroad scope of the present invention.

Example I A catalyst comprising 0.375 weight percent platinum, 3.5weight percent fluoride, 0.1 weight percent chloride on a gamma-aluminasupport was placed in an isomerization zone. A charge stock comprising100% o-Xylene was charged to the isomerization zone at a liquid hourlyspace velocity of 5.0, a hydrogen to hydrocarbon mole ratio of 10:1, apressure of 20.4 atmospheres and a temperature of 482 C. Charge stockand product analyses are shown in Table I below.

TAB LE I 6 tive to meta and each other. Ethylbenzene is not convertedsince the amount in the charge is below the equilibrium Char e Productvalue. As used herein, C ring retention is the percent of EthylbenzeneL2 the original C -aromat1cs rema1n1ng as C -armat1cs 0r m 2 convertedto naphthenes wlthm the reactor. mgiylene- 38. 9 0- yene 46- C-uaphthenes 0. 6 Example In Other nonaromatics and benzene. 'oluene 1.0A catalyst comprlsmg 0.375 welght percent platlnum, Q3 2.3 weightpercent chloride on a gamma-alumina sup- Total, wt. percent 100.0 100.0port was placed in the isomerization zone. A charge Caring retention 913stock containing 23.6 weight percent ethylbenzene was charged to theisomerlzatlon zone at varying space velocihes, a hydrogen to hydrocarbonmole ratio of 5:1, a AS (2311 be $6611 from Tablfi t l w naphtheneconpressure of 10.2 atmospheres, and a temperature of centrations, avery selectlve reaction occurs with substan- 400 C. to 402 C. tiallyequlhbrium conversion of para-xylene belng ob- The liquid hourly spacevelocities, as mentioned above tamed. The ethylbenzene which 1s producedis far less were varied for each of the tests to vary conversions thanequllibrium amounts. In general, the rate of reaction as shown below.

TABLE 111 Product Charge stock Test 1 Test 2 Test 3 Ethylbenzene 23. 614. O 9. 9 16. 8 p-Xylene 10. 6 18. 3 19. 6 17. 5 m-Xylene 56. 1 42. 241. 5 43. 6 o-Xylene 9. 1 16. 2 17. 6 14. 9 Cg-uaphthenes 0 6. 1 6. 5 5.1 Other nouaromatics and benzenes 0. 5 2. 0 2. 9 1. 3 Toluene ,r 0. 1 0.4 0. 8 0. 3 011+ 0.8 1.2 0. 5

Total, wt. percent 100. 0 100.0 100. 0 100. 0

Total C -naphthenes, Wt. percent of charge... 6. 1 6. 5 5. 1 Liquidhourly space velocity 2 1 3 Total xylenes, wt. percent of charge 76. 778. 5 76. 0 Percent para/total xyleues 23. 9 24. 9 23. 0 Percent ortho/total xylenes 21. 1 22. 4 19.6 05 ring retention 96. 9 95. 2 98. 0

involving ethylbenzene toward equilbrium is slower than the rate ofxylene isomerization. This shows that the presence of naphthenes in asubstantial concentration, as in the range of 2 to 9 weight percent isnot necessary to isomerize a pure xylene feedstock.

Example 11 A catalyst comprising 0,375 weight percent platinum, 1.73weight percent fluoride, 0.39 weight percent chloride on a gamma-aluminasupport was placed in an isomerization zone. A charge stock containing aminor amount of ethylbenzene, namely 5.2 weight percent was charged tothe isomerization zone at a liquid hourly space velocity of 2.0, ahydrogen to hydrocarbon mole ratio of 6:1, a pressure of 12.1atmospheres and a temperature of 398 C. Chloride addition to the feedwas maintained at 0.0025 weight percent of the feed by utilizingt-butylchloride. Charge stock and product analyses are shown in Table IIbelow.

TABLE 11 Charge stock Product Ethylbenzene. 5. 2 5. 2 pQiylcne-.-

11.5 19.1 n1-Xylene 71. 3 48. 4 o-Xylene 11.0 16. 5 Cg-naphthenes 0 8. 6Other nonaromaties and benzene 0. 1 1. 4

Toluene r 0.3 09+ O. 5

Total, wt. percent 100.0 100.0

Percent para/total xylenes 22. 8 Percent ortho/total xylenes- 19. 6 (3ring retention (percent) 97. 8

As can be seen from the product analyses, ethyl-benzene concentrationremained the same but the orthoand para-xylene have come to substantialequilibrium rela- For all the tests shown, the paraand ortho-xylene arein substantial equilibrium with the meta-xylene.

Example IV A catalyst comprising 0.375 weight percent platinum, 1.7weight percent fluoride on a gamma-alumina support was placed in theisomerization zone. A charge stock containing a high ethylbenzeneconcentration, namely 43.0 weight percent was charged to theisomerization zone at a liquid hourly space velocity of 2.0, a hydrogento hydrocarbon mole ratio of 6:1, a pressure of 11.9 atmospheres and ata temperature of 405 C. Chloride addition to the feed was maintained at0.0025 weight percent (of the feed). Charge stock and product analysesare shown in Table IV below.

TAB LE IV Charge stock Product Ethylbenzene 43. 0 23. 5 1e 8. 1 15. 641. 3 36. 0 7.1 13. 3 C -naphthenes 0 8. 3 Other nonarornatics andbenzene 0. 4 2. 4 Toluene 0. 1 0. 3 CH" 9. 6

Total, Wt. percent 100.0 100. 0

Percent para/total Xylenes 24. 1 Percent ortho/total xylenes 20. 5 Totalxylenes, weight percent of feed. 56. 5 64. 9 Cg ring retention 96. 8

The operation resulted in an appreciable conversion of the ethylbenzeneto mixed xylenes which, in a recycle operation, would be more eflicientyet because the C naphthenes have already been produced in essentiallyequilibrium concentration and would not subtract further from the C-aromatics in the feed. Substantially equilibrium concentration ofparaand ortho-Xylene was observed.

Example V The same catalyst utilized for the preceding example wasutilized for a charge stock containing a slightly higher concentrationof ethylbenzene, namely 46.0 weight percent. This charge stock wascharged to the isomerization zone at a liquid hourly space velocity of2.0, a hydrogen to hydrocarbon mole ratio of 6:1, a pressure of 12.1atmospheres, and a temperature of 403 C. Chloride addition to the feedwas maintained at 0.0025 weight percent (of the feed). The total weightpercent C -naphthenes in the efiluent was 6.1 weight percent. Chargestock and product analyses are shown in Table V below.

TABLE V Charge stock Product Ethylbenzene 46. 31.0 p-Xylene 8. 1 14. 5m-Xylenem 38. 7 33. 8 o-Xylene 6. 7 12. 2 Cs-naphthenes 0 6. 1 Otherncnaromatics and benzene 0. 2 1. 5 Toluene O. 1 0. 3 C 0. 2 0. 6

Total, wt. percent 100. 0 100. 0

Percent para/total xylenes 24. 0 Percent ortho/total xylenes 20. 1Weight percent total xylenes Based on charge 53 5 60. 5 08 ringretention 98. 1

Again, the conversion of the ethylbenzene to mixed xylenes is efficientconsidering also the C -naphthenes found, and the paraand ortho-xyleneare in substantial equilibrium with the meta-xylene.

Example VI A catalyst comprising 0.375 weight percent platinum, 1.7%chloride and 0.5% fluoride on a gamma-alumina support was placed in theisomerization zone. The charge stock containing 100.0 weight percentethylbenzene was charged to the isomerization zone at a liquid hourlyspace velocity of 1.0, a hydrogen to hydrocarbon mole ratio of 5:1, apressure of 6.8 atmospheres and at a temperature of 401 C. Chlorideaddition to the feed was maintained at 0.02 weight percent (of thefeed). Charge stock and product analyses are shown in Table VI below.

As can be seen from the product analysis, it is apparent that thepresent catalyst and conditions of operation are greatly superior inaccomplishing isomerization of any C -aromatic, including ethylbenzene,in spite of the low naphthene content of the system. It should also benoted that high yields of xylenes having substantially equilibriumconcentration of paraand ortho-xylene were obtained.

Example VII The feed stock of Example VII was processed over the samecatalyst at the same conditions as Example VI except that thetemperature was about 405 C. and the chloride addition to the feed washeld at 0.04% by weight. Charge and product are shown below.

TABLE VII Charge stock Product E tllylbenzene 100. O 75. 4 pXylene 3. 2m-Xylene. 9. 6 o-Xylene 4.5 C -naphthenes 1. 4 Other nonaromatics andbenzene. 4. 9 Toluene 0.4 09+ 0.6

Total, wt. percent 100. 0 100. 0

C3 ring retention, percent 94. 1

It will be noted that a greater ring loss and lesser conversion resultedthan in Example VI, attributable to an insufiicient concentration of C-naphthenes in the system. This results even though the change inprocessing conditions appears to be relatively insignificant.

As noted in these examples, isomerization of a particular xylene(Example I) to the other xylenes is accomplished readily withoutnecessitating the presence of significant amounts of C -naphthenes. Onthe other hand, when ethylbenzene is to be converted to xylenes in anefiicient manner, concurrent with establishing the essentialisomerization equilibrium among the xylenes, some C napl1- themes arerequired.

In a typical recycle operation in which an average C aromatic fractionincluding ethylbenzene is to be converted entirely to specific xyleneisomers, the combined feed rate through the isomerization zone isseveral times larger than the fresh feed. Consider, for example, theconversion of the following feed to para-and/or ortho-xylene.

Fresh feed composition, wt. percent:

Ethylbenzene 24.0 Para-xylene 20.5 Meta-xylene 40.5 Ortho-xylene 15.0

When 100 weight units of this feed is supplied to a reaction/separationcircuit which includes a crystallizer for para-xylene removal and afractionator for ortho-xylene removal, and these removal devices arethen operated to recover a predetermined fraction of the specificisomers desired, the following yields are obtainable.

Case 1 2 3 4 5 Percent recovery of para in crystallizer feed 62. 4 60. 961.2 61.4 38. 1 0 Percent recovery of ortho in xylene fractionator feed0 30 60 95 05 Combined teed ratio, based on unit weight of fresh feed6.8 5.0 3. 9 3. 1 3. 7 5. 6 Yields, wt. percent:

Para-xylene. 82. 6 61. 8 49. 9 41. 2 30. 1 0

Ortho-xylene. 0 25. 4 40. 1 50. 8 60. 2 85. 7

C -naphthenes percent 4. 7 5. 5 5. 9 6. 1 5. 0 5. 2

C3 ring retention per pas 97 07 07 97 97 07 Reactor outlet conditionPressure, atm. gauge 10. 2 10.2 10. 2 10.2 10.2 10.2

Temperature, C 409 407 406 405 406 408 It will be noted that thecombined feed ratio to the isomerization zone varies from about 3.1 toabout 6.8 times the fresh feed. The C -naphthene concentration requiredin the reaction zone varies somewhat because the extent of conversionrequired per pass for the ethylbenzene depends upon the combined feedratio. In all cases the C -naphthene level is chosen to result in a Cring retention of 97%. Small changes in pressure and/ or temperatureaccomplish this control because the C -naphthenes are in essentialequilibrium with the C -aromatics at the reactor outlet. Thesenaphthenes are automatically returned to the reactor with theunconverted ethylbenzene and xylenes to prevent the formation ofadditional amounts of naphthenes from the fresh feed. It is to berealized that some naphthenes must be formed in the reactor to oiisetlosses incurred elsewhere in the total system. It has thus been shownthat the presence of about 2 to about 9 weight percent naphthenes iscritical to the eifective isomerization of ethylbenzene in both arecycle process and a once-through operation.

We claim as our invention:

1. An isomerization process for the production of a specific Xyleneisomer which comprises contacting hydrogen and a C -aromatic chargestock containing ethylbenzene at a concentration greater thanequilibrium with respect to the xylenes present and containing C-naphthenes at isomerization conditions in a reaction zone, with acatalytic composite of alumina combined with about 0.01% to about 1.0%,by weight, of a platinum component and about 0.1% to about 5.0%, byweight, of a halogen component, separating a specific xylene isomer fromthe resulting reaction product effluent and providing a hydrocarbonstream containing unreacted ethylbenzene, C -naphthenes, and xyleneisomers, and recycling said hydrocarbon stream to said reaction zone;said process further characterized in that said isomerization conditionsare selected to maintain a c -naphthene content in said C -arornaticcharge to said reaction zone of from 2.0% to about 9.0% by weight, ofthe C -aromaties in said charge, said isomerization conditions includingan LHSV of about 0.2 to about 8.0, a temperature of about 370 C. toabout 450 C., a pressure of about 3 atmospheres to about.20 atmospheres,and a hydrogen concentration in a mole ratio of about 2.0:1 to about20.011 with respect to said C -aromatic charge.

2. The process of claim 1 further characterized in that said specificxylene isomer is para-xylene.

3. The process of claim 1 further characterized in that said specificXylene isomer is ortho-xylene.

4. The process of claim 1 further characterized in that from about 1.0to about 10 00 p.p.m., by weight, of halogen is added to said C-aromatic charge.

References Cited UNITED STATES PATENTS 2/1963 Berger. 4/1968 Lovell etal.

